This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
There are today many different kinds of content distribution networks, such as for example Peer-to-Peer (P2P) networks that hereinafter will be used as a non-limitative example.
FIG. 1 illustrates a typical prior art P2P network 100. The P2P network 100 comprises a plurality of peers 110A-110D (that may share reference number 110 when referred to as a group), functionally connected through a network 120, which commonly is the Internet. A first peer 110A stores a content 130 that it is willing to share with the other peers 110B-110D in the P2P network 100. Without going into specific details of just how a peer 110 may detect content on another peer 110, the other peers 110B-110D may download the content from the first peer 110 A.
It is possible that a large number of other peers want to download the content from the first peer 110A. However, when a peer has downloaded one part of a content file, it can share this part with further peers that then may download the part from either the first peer 110A or the peer that just downloaded the part. It will be appreciated that this system can reduce the load of a peer that initiates the content in the network 100. The more peers that download a content file, the more peers may offer the content file to further peers, which means that the system can be easily scalable to a large number of peers.
An intrinsic problem is the initial seed of content. In standard use of a P2P network 100, when a new file is shared by the first peer 100A, the number of peers that request the new file increases slowly, which means that first peer (also called “initial seeder”) only serves few peers. Then, once the demand for the content has grown, a plurality of peers has already downloaded the content and can redistribute it. The bootstrap is thus slow. This is particularly problematic in the case of fresh content or pseudo-live content, i.e. content distributed with a small time shift. In “Incentives Build Robustness in BitTorrent”, 2003, Bram Cohen proposes a solution that gives priority to the download of the content file that is the least widely distributed of the requested content files. This solution mitigates the problem, but does not solve it, but it does not encourage sharing of the downloaded file.
Greedy behaviour worsens this problem: some peers want to download the content without participating in its redistribution. If too many peers behave this way, then the P2P network is not able to scale up well to the point where P2P technology is efficient. In “An Incentive Mechanism for P2P Networks”, 24th International Conference of Distributed Computing Systems (ICDCS'04), IEEE Computer Society, 1063-6927/04, Richard Ma et al. provide an incentive mechanism for partially limiting the greedy behaviour by giving those who participate in the redistribution priority in the queue of uploaders. Another such solution is described in EP 1752925 in which each peer has a credit value that is increased when content is uploaded from the peer and decreased when the peer downloads content. These solutions also mitigate the problem but do not solve it.
The so-called flash crowd behaviour further worsens this problem. This happens when new content, which is much sought after, is shared and a great number of peers try to download it at essentially the same time. The initial peer cannot respond to all requests. Existing incentive mechanisms do not help much in this case.
It will therefore be appreciated that there is a need for a solution that can allow to reduce the overload of the initial seeder and to encourage peers to offer upload bandwidth for other peers. This invention provides such a solution.